1. Field of the Invention
The present invention relates to a catalytic converter or diesel particulate trap used to clean the exhaust gas of an internal combustion engine and more particularly, to a catalytic converter or diesel particulate trap having a metallic casing with a monolithic catalytic element or diesel filter securely but resiliently mounted within the casing by an mounting composite comprised of a flexible, resilient, intumescent sheet which has its edges normal to the exhaust flow.
2. Description of the Prior Art
Catalytic converters are universally employed for oxidation of carbon monoxide and hydrocarbons and reduction of the oxides of nitrogen in automobile exhaust gas. Diesel particulate traps are used to collect soot generated by diesel engines. Collected soot is periodically burned off with a gas burner or electrical heater. Due to the high temperatures encountered in either of these environments, ceramic has been the logical choice for catalyst supports or diesel filters.
Ceramic monoliths tend to be frangible and have coefficients of thermal expansion differing markedly from their metal, usually stainless steel, containers. Thus, the mounting means of the ceramic monolith must provide resistance to mechanical shock due to impact and vibration and to thermal shock due to thermal cycling. Both thermal and mechanical shock may cause deterioration of the ceramic support which, once started, quickly accelerates and ultimately renders the device useless. Intumescent sheets that have been found adequate as mounting materials for this purpose are disclosed in U.S. Pat. Nos. 3,916,057, 4,305,992 and U.K. Patent No. 1,513,808.
Intumescent sheet mounting materials do an adequate job of holding the ceramic monolith or diesel particulate filter in place while resisting erosion at moderate exhaust temperatures (less than 700.degree. C.), and moderate pressure pulsations of the exhaust gas, as in six and eight cylinder engines. However, with the trend towards smaller, four cylinder engines running at higher rotation velocities and with the advent of catalytic converters in Europe, with their high speed driving conditions, present mounting materials are being subjected to much higher exhaust temperatures and more severe pressure pulsations. Under these conditions, over a period of time, present mounting materials can be eroded.
It is therefore an object of this invention to provide a ceramic monolith mounting composite for catalytic converter elements or diesel particulate traps which can withstand the erosion effects of higher exhaust temperatures and more severe pressure pulsations associated with present operating conditions.